The present invention relates to a distributed file system (DFS), a distributed file system server, and a method for accessing the distributed file system. More specifically, the invention relates to the distributed file system that distributes a file to a plurality of servers on a network, for storage, thereby constituting a single file system, a server in the distributed file system, and the method for accessing the distributed file system.
As file systems using the network, the file systems such as a file system referred to as a common Internet file system (CIFS) and a network file system (NFS) constructed on a UNIX® operating system (OS) are known. These file systems are centralized file systems, in which a single file system is constituted by a single server. In these systems, file entities reside on a specific server. When accessing a file in each of these file systems, the client first accesses a server on which the targeted file resides, employing a protocol for the file system. At this point, in order to specify the file on the server, the client uses a directory structure.
In contrast therewith, in the DFS in an “OceanStore”, which is a utility infrastructure designed to span the globe and provide continuous access to persistent information, when accessing a file, the client employs an identifier for the file uniquely assigned by a global unique identifier (GUID) system, instead of specifying the server and a pathname for the file. In the DFS, the entity of the file resides on a plurality of DFS servers on the network. The entity of the file does not need to be held by a single DFS server, and may reside on other server as a copy. Alternatively, the file may be divided into some portions; one of the divided portions of the file, referred to as a fragment, may reside on a single DFS server, and remaining fragments may reside on other DFS server or servers.
When accessing a file in the DFS to refer to or perform writing to the file, the client specifies the GUID for the file for identification of the file, thereby accessing one of the servers on the network.
As a prior art associated with the present invention, a system equipped with a communication interface for connection to all kinds of user data from a storage server is disclosed in U.S. Pat No. 6,446,141, for example.
The DFS has characteristics different from those of the network file systems such as the NFS and the CIF. Thus, in order to access a file in the DFS, or a DFS file, a protocol dedicated to the DFS must be employed. For this reason, a conventional client that uses only the protocol for the NFS or the CIFS cannot access the DFS file. Thus, it was necessary to make a modification on a client side, such as an improvement in a program used so far, to accommodate the DFS. In other words, in order to function as a DFS client in the DFS system, there was a need for the client in the centralized file system, which uses the conventional protocol, to modify the program.